The present invention relates generally to take-out apparatus used in conjunction with a plastics molding machine for removing molded articles from the machine. The present invention particularly relates to removing a large number of articles such as preforms intended for use in the manufacture of plastic bottles from the injection molds using a removal apparatus which does not form a part of the mold in which the preform is initially made.
In the manufacture of plastic articles in injection molding machines, an enhanced production rate is often achieved by simultaneously molding in a single machine a large number of the articles. The rate of production can be measured by the number of articles manufactured by each cycle of the machine divided by the time for each cycle. A number of factors impact on the production rate such as the capacity of the molding machine to plasticize the amount of plastic resin to the appropriate fluid state to permit formation by injection of the number of articles intended during each cycle of the machine.
An important limiting factor is the time required to cool the articles once formed in the molding machine of the plasticized or molten resin, The resin forming the articles must cool from the injection temperature, which is typically several hundred degrees Celsius, down to a temperature at which the articles will remain stable in form as they are handled in subsequent processes, which is generally a temperature less than 100.degree. C. Of course, the exact temperatures are a function of the particular resin employed and well understood by those experienced in the art of injection molding.
The cooling time is a function of the amount of resin employed in the articles and in the thickness of the articles. As the thickness of the articles increases, the thermal conductivity of the plastic, which is generally poor, inhibits the flow of heat from interior portions of the article thus extending this cooling time. It has been recognized that the articles need not be fully cooled while in the injection molding machine, particularly where the articles are going to immediately be subject to a reforming process such as blow molding, so long as the surfaces of the articles are cooled sufficiently from the molten state to a maximum handling temperature, i.e., the temperature at which no appreciable distortion of the molded article occurs as a result of the removal of the article from the injection mold. This time can be minimized by handling the articles so that they experience a balance of any forces which could possibly cause appreciable distortion. For preforms used in the blow molding of plastic bottles, this minimization of distortional forces can be accomplished by molding the preforms in a vertical orientation rather than a horizontal orientation thereby minimizing gravitationally induced deflection of the preform.
Many of the vertically orientated preform molding machines are merely part of integrated injection blow molding machines in which the preform is directly transferred from the injection mold to a blow mold often by way of an intermediate temperature modification station all existing in a single machine. In such machines the transfer of the preform to subsequent stages of the machine occurs with the aid of a portion of the mold, often referred to as a thread split, which carries the preform from station to station within the machine, never releasing the molded article until the blow molded article is completed. Examples of such machines are found in U.S. Pat. Nos. 4,105,391; 4,344,749; and 4,747,769.
Some of the vertically orientated preform molding machines are coupled to separate blow molding or other apparatus such that the injection molded preform is transferred from the injection mold to a subsequent processing machine using a transfer or removal apparatus which does not form a part of the mold in which the preform is initially made. Examples of such machines are found in U.S. Pat. Nos. 4,197,073 and 4,209,290. In such machines, the overall rate of production of the molding machine is diminished by the amount of time required for the removal apparatus to enter the machine once the mold has opened a distance sufficient to permit the entry of the cooling apparatus. The rate of production of such molding machine could be increased were the preform removal apparatus designed to enter the molding machine while the article is being molded and to exit the molding machine immediately upon release of the molded article from the article-forming mold portion of the machine.